1. Field of the Invention
The present invention relates to an optical apparatus, and more particularly, to an optical apparatus having a function to prevent an image blur caused by hand fluctuation or the like.
2. Related Background Art
As an apparatus for preventing faulty photography due to the hand fluctuation of photographer there are many proposals of such structure as to detect fluctuation caused by the hand fluctuation, displace a correction lens in accordance with a detection value of the fluctuation, and correct a change of the optical axis of an image.
Examples of the correction method by the correction lens include a method for eccentrically moving the optical axis of a part of a taking lens in parallel (or shifting it), a method for inclining the optical axis thereof (or tilting it), a combination method of the foregoing, a method for locating a variable angle prism (VAP) in a front part of a photographic optical system, and so on.
Specially explained among them is the method for eccentrically moving a part of the taking lens. A base member of a fluctuation correction unit holds an interconnecting member free to move in a direction perpendicular to the photographic optical axis (for example, in the pitch direction). The interconnecting member holds a correction lens frame, to which the correction lens is fixed, free to move in a direction perpendicular to the foregoing direction (for example, in the yaw direction). By this arrangement, the correction lens frame is held on the base member so that the correction lens frame can freely move both in the pitch direction and in the yaw direction, perpendicular to the optical axis, relative to the base member.
An actuator for driving the correction lens is arranged in such a manner that voice coils each corresponding to the pitch direction and the yaw direction perpendicular to the photographic optical axis as discussed above are fixed to the correction lens frame and a pair of a yoke and a magnet are fixed to the base member in correspondence to each of these voice coils.
For detecting an eccentric position of the correction lens in each of the pitch direction and the yaw direction, the correction lens frame holds light projecting elements (or light receiving elements) and the base member holds light receiving elements (or light projecting elements) corresponding thereto, whereby the position of the correction lens is detected in accordance with quantities of light received by the light receiving elements for the light from the light projecting elements. Accurate drive control of the correction lens is realized based on the position information.
As for the power supply for the fluctuation correction apparatus, some cameras use the same power supply in the camera body. Other cameras have a dedicated power supply for correction of fluctuation in order to perform the correction of fluctuation at the same time as autofocusing and aperture drive being functions of the camera body in view of the problem of power or the problem concerning the camera system.
An example of actuation of the actual fluctuation correction apparatus is to turn on a fluctuation correction start switch by an external operation to supply the power to the fluctuation correction control circuit, fluctuation sensor, and correction optical system driving means and to start the fluctuation correction operation. Another example is to start the fluctuation correction by an external switch and a release signal of camera, that is, to start it when the shutter release button of camera is half depressed in the on state of the external switch. For stopping the fluctuation correction, the external switch is turned off, or, even in the case of the external switch being in the on state, the shutter release button of camera is fully depressed to complete exposure or the half-press state of the shutter release button is released and then a lapse of a predetermined time is awaited, thus stopping the fluctuation correction. On this occasion, the correction optical system is arranged to drive the optical axis up to the position where it is coincident with the optical axis of the other taking lens, and the power supply is stopped after the correction optical system is fixed by a mechanical lock means.
Describing the detection of fluctuation in further detail, a sensor such as an angular acceleration meter or an angular velocity meter detects the fluctuation of the camera body and the lens barrel due to the hand fluctuation and an angular displacement is electrically or mechanically calculated based on a signal from the sensor.
Among such sensors, a vibratory gyro for detecting the angular velocity is recently drawing attention because of the advantages of its simple structure, compact size, and low price.
Briefly explaining the principle of operation of the vibratory gyro, a tuning bar in a shape of a circular cylinder or a prism several mm thick and several cm long approximately is vibrated at several kHz by an electrostrictive element. When rotation is applied there, force appears in the direction perpendicular to the direction of the vibration. This force is the Coriolis force, which is proportional to the angular velocity. Another electrostrictive element different from that for drive detects strain occurring because of the Coriolis force in the direction different from the direction of vibration. An output from the electrostrictive element is taken out as an ac voltage, is synchronously detected using the voltage applied to the driving electrostrictive element as a reference signal, and is let to pass through a low-pass filter. This obtains an output of a dc voltage proportional to the angular velocity of rotation.
Presently, the tuning bar, driving circuit, and detecting circuit are packed in a package of approximately 2.times.1.times.1 cm, which is commercially available. Thus, the reduction in the size and price of the vibratory gyro greatly contribute to today's wide-spread use of the fluctuation correction apparatus at the consumer-oriented product level.
When the fluctuation correction apparatus is used in a still camera or in a taking lens for a still camera, a capability of correcting the fluctuation during exposure is important. Describing in more detail, the fluctuation correction apparatus needs to operate continuously between opening and closing of the shutter, and thus, in the case of the single-lens reflex camera, the fluctuation correction apparatus usually continues operating during a period from the point of determining the composition as viewing a finder image via mirror-up and opening of shutter to closing thereof.
However, the conventional example using the vibratory gyro as a fluctuation sensor had the following problem. In the conventional example, the detection of fluctuation is carried out by vibrating the tuning bar and amplifying the small strain caused by the angular velocity of rotation, as described above. The vibration or sound during the mirror-up operation or during the shutter operation propagates in structural members or in air to generate an error signal in the vibratory gyro, which results in driving the correction optical system in accordance with a signal indicating fluctuation that is not actually occurring and thus the resulting photograph has image blur.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide an optical apparatus that can prevent the operation of camera from negatively affecting the fluctuation detecting means.